diff --git a/lix/legacy/nix-build.cc b/lix/legacy/nix-build.cc
index db0cc80cc..c11ec1b9a 100644
--- a/lix/legacy/nix-build.cc
+++ b/lix/legacy/nix-build.cc
@@ -503,11 +503,13 @@ static int main_nix_build(AsyncIoRoot & aio, std::string programName, Strings ar
         auto rcfile = (Path) tmpDir + "/rc";
         auto tz = getEnv("TZ");
         std::string rc =
-            fmt("%1%"
+            fmt("#!%1%\n"
+                "%2%"
                 // always clear PATH.
                 // when nix-shell is run impure, we rehydrate it with the `p=$PATH` above
                 "unset PATH;"
                 "dontAddDisableDepTrack=1;\n",
+                *shell,
                 (pure ? "" : "[ -n \"$PS1\" ] && [ -e ~/.bashrc ] && source ~/.bashrc; p=$PATH; "));
         rc += structuredAttrsRC;
         rc += fmt(
diff --git a/tests/functional/nix-shell/shell.nix b/tests/functional/nix-shell/shell.nix
index 1beeb3357..dc756d0f5 100644
--- a/tests/functional/nix-shell/shell.nix
+++ b/tests/functional/nix-shell/shell.nix
@@ -63,14 +63,16 @@ let pkgs = rec {
 
   foo = runCommand "foo" {} ''
     mkdir -p $out/bin
-    echo 'echo ${fooContents}' > $out/bin/foo
+    echo '#!${shell}' >> $out/bin/foo
+    echo 'echo ${fooContents}' >> $out/bin/foo
     chmod a+rx $out/bin/foo
     ln -s ${shell} $out/bin/bash
   '';
 
   bar = runCommand "bar" {} ''
     mkdir -p $out/bin
-    echo 'echo bar' > $out/bin/bar
+    echo '#!${shell}' > $out/bin/bar
+    echo 'echo bar' >> $out/bin/bar
     chmod a+rx $out/bin/bar
   '';
 
@@ -83,7 +85,8 @@ let pkgs = rec {
   # ruby "interpreter" that outputs "$@"
   ruby = runCommand "ruby" {} ''
     mkdir -p $out/bin
-    echo 'printf %s "$*"' > $out/bin/ruby
+    echo '#!${shell}' > $out/bin/ruby
+    echo 'printf %s "$*"' >> $out/bin/ruby
     chmod a+rx $out/bin/ruby
   '';
 
diff --git a/tests/functional/user-envs.builder.sh b/tests/functional/user-envs.builder.sh
old mode 100644
new mode 100755
index 5fafa797f..b690b1248
--- a/tests/functional/user-envs.builder.sh
+++ b/tests/functional/user-envs.builder.sh
@@ -1,3 +1,4 @@
+#!/usr/bin/env bash
 mkdir $out
 mkdir $out/bin
 echo "#! $shell" > $out/bin/$progName